A digital TV decoder can be divided into five modules: demodulation; MPEG transport packet parser (TPP); MPEG audio; MPEG video; and a RISC micro-controller.
A MPEG2 transport stream parser (TPP) receives the MPEG transport stream and selects video, audio or services information packets. After decoding, the packets are stored in memory buffers to form a data stream. The audio decoder processes the MPEG audio stream and produces analog audio signal. The video decoder decompresses the MPEG video and generates a video sequence.
A transport packet (FIG. 1) contains 188 bytes. The packet is divided in two parts a 32 bits header and 184 bytes of payload. The transport header contains different fields (PID, payload unit start indicator, adaptation field flags, Continuity Counter index) that will allow the transport packet parser to do a coarse filter. After the transport header, the packet can contain an adaptation field of variable length or a payload. Some of these payloads will themselves start with a header (PES header) which has also a variable length (see FIG. 1). The PES header in MPEG2 standard can be bigger than a packet (overflow on the next packet).
The state of the art for MPEG2 transport stream system analyzer consists of chip set solution including a complete transport stream hardware analyzer and a micro-processor. Video and audio decoder are in a separate device as shown in the FIG. 2. The transport stream parser is in charge of the transport stream full analysis (approximately 70 k gates) with the current approach leaving to the CPU the tasks of directing the data towards the right destination and controlling the different modules. Another solution would be to implement all the transport analysis in software. This will require much higher CPU power processing.